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Disease management

Stamp out disease! What do you need to know?

Developing an Integrated Disease Management strategy for your farm

Effective disease management should be integrated within the management of the whole farm, focusing on the host, the potential pathogen, and the environment. The implementation of basic disease management strategies, even where a significant disease problem is not evident, will reduce the risk of future outbreaks.

To determine what diseases are present and where they occur, conduct early and late season disease surveys and record findings to allow comparison over time. Farm staff should be trained to look for and report unusual symptoms.

Pathogen control

Come Clean Go Clean:

Preventing a pathogen from entering your farm is far easier than managing a disease. Managing machinery movements within the farm and implementing a strategy for ensuring clean movement of machinery onto and around the farm will minimise the risk of moving disease onto or off your from, or from one field to another. It also pays to minimise spillage and loss when transporting modules, hulls, cotton seed or gin trash. More information on Come Clean Go Clean can be found on the biosecurity page of this site, and in the CottonInfo Come Clean Go Clean fact sheet.

Control alternative hosts and volunteers:

Implementing a host free period prevents build up of disease inoculums and carryover of disease from one season to the next. The pathogens that cause Verticillium wilt, Fusarium wilt, black root rot, Tobacco Streak virus and Alternaria leaf spot can also infect common weeds found in cotton growing areas. A host free period is particularly important in the control of disease such as Cotton Bunchy Top that can only survive in living plants. Controlling alternative hosts, especially cotton volunteers and ratoons helps reduce the risk of disease outbreak.

Crop residues:

Crop residues can be managed to minimise carryover of pathogens into subsequent crops. Crop residues should be incorporated as soon as possible after harvest, except where Fusarium wilt is present. Where Fusarium wilt is present, residues should be slashed and retained on the surface for at least one month prior to incorporation. Fusarium wilt can also survive and multiply on the residues of non host crops such as cereals. Current recommendations are that residues should be incorporated or removed as soon as possible after harvest.

Crop rotations:

Use rotation crops that are not hosts for the pathogens requiring control. The Cotton Rotation Finder (listed under tools, below) can assist in understanding how rotation crops will impact disease load.

Insect vectors:

Diseases caused by a virus or phyoplasma can often be prevented by controlling the vector that carries the pathogen. For example, Cotton Bunchy Top (CBT) can be transmitted by aphids feeding on infected plants then migrating to healthy plants.

Managing the host crop:

A healthy crop is more able to express natural resistance to disease. Strong seedling vigour can also assist the plant to cope with pathogens. A balanced approach to crop nutrition, especially with nitrogen and potassium, will make plants less susceptible to disease. Both deficiencies and excesses can create favourable conditions for the development of diseases such as Verticillium wilt and Alternaria leaf spot. Excess nitrogen greatly increases the risk of boll rot.

Resistant varieties:

A particular plant may be immune, resistant or susceptible to disease. The term ‘tolerant’ implies reasonable yield performance despite the presence of disease. Disease risk is greater in back to back fields increasing the importance of planting resistant varieties. F-rank and V-rank are used to describe the Fusarium and Verticillium disease resistance rankings.

Managing environmental conditions:

Altering row or plant spacing, changing irrigation method or frequency, or changing sowing date are means of manipulating environmental conditions to be less conducive to infection and disease spread in the host plant.

Planting:

Planting into well prepared, firm, high best will optimise stand establishment and seedling vigour. Carefully positioned fertiliser and herbicides in the bed prevents damage to plant roots. Fields should have good drainage and not allow water to back-up and inundate plants. Ideal soil temperatures for cotton establishment are 16–28 degrees (celcius). Temperatures below this result in slow emergence and increased chance of attack from soil pathogens and insects. Where possible delay planting until conditions are suitable.

Irrigation scheduling:

Applying water prior to planting provides better conditions for seedling emergence than water after planting, as the water can drop the soil temperature further. Root systems weakened by disease can show water stress early in the season, and should be irrigated accordingly. Waterlogging should be avoided, particularly late in the season when temperatures have cooled.

Agronomic management:

High planting rates can compensate for seedling mortality but a dense canopy favours development of bacterial blight, Alternaria leaf spot and boll rots. Avoid rank growth and a dense canopy with optimised nitrogen and water and the use of growth regulators where required. Considering an early planting date, or a delayed harvest, may be an appropriate response to various disease problems. In fields where Fusarium wilt is present avoid inter row cultivations after seedling stage as mechanical damage to the roots provides a site for infection by the pathogen.